This invention relates to the preparation of activated carbons and is more particularly directed to a process for enhancing the capacity of carbon for storage of hydrogen or other gases.
Activated carbons are high-surface-area materials that possess surface functional groups that can be manipulated by chemical treatment. As a class of sorbents, activated carbons are an attractive medium for storage of alternative fuels such as hydrogen and methane. The combined effects of high surface area and surface functional groups can lead to an enhanced storage capacity.
Hydrogen storage in carbon has been described, e.g., in U.S. Pat. No. 4,716,736. However, not all carbons possess the capability of having their storage capacity enhanced significantly, and in the past this capability has not been understood or predictable.
A previous publication, Agarwal et al., "Effect of Surface Acidity of Activated Carbon on Hydrogen Storage", Carbon, Vol. 25, No. 2, 219-226 (1987) describes hydrogen adsorption studies at 78 K. and pressures up to 40 atm using a variety of commercially available active carbons. Surface modification consisted of increasing the surface acidity by an oxidation treatment. It was noted that the amount of hydrogen adsorbed increased with increased surface acidity of the active carbons. However, this early treatment failed to recognize that the nature and quantity of impurities in the starting carbon material were of any significance, and thus offered no suggestions either as to selection of the carbon source material, or as to the treatment of the material prior to oxidation.